1. Field of the Invention
This invention relates to techniques for developing certain correction factors and using these correction factors in analyzing the vibration frequency and displacement characteristics of a piezoelectric material. Such analysis is preferably carried out during the design of a piezoelectric device incorporating the piezoelectric material before production of the piezoelectric device. The design may also include additional design-based analysis such as determining whether the device and its electrodes exhibit appropriate stiffness characteristics.
2. Description of the Related Art
A wide variety of piezoelectric devices are used in various electronic applications. One common type of piezoelectric device is a crystal resonator. A typical crystal resonator includes a layer of crystalline piezoelectric material having opposite faces, each having a corresponding electrode bonded thereto to sandwich the piezoelectric material between the electrodes. The crystal resonator vibrates in response to an electrical stimulus applied to the electrodes. The vibration induces a highly stable electrical oscillation across the electrodes that is useful for timing other devices.
For a piezoelectric device to operate properly, it is important for its vibration frequency and displacement characteristics to fall within design specifications. For example, if the elastic properties of its piezoelectric material falls outside design specifications, the piezoelectric device may not have the desired oscillation frequency or magnitude response. Unfortunately, it has proven very difficult to precisely determine such elastic properties of piezoelectric materials. One reason for this difficulty is that there is considerable interplay between the various elastic properties of a piezoelectric material.
Due to such difficulties, piezoelectric devices generally are formed in a rough state that is not guaranteed to be within final design specifications. The piezoelectric devices may then be brought into final design specifications by adding or removing material from the piezoelectric device. In one conventional approach, material is added or removed from electrodes. In another conventional approach, stiffening electrical fields are applied to a piezoelectric device during operation. In a third conventional approach, a piezoelectric device is stiffened to reduce acceleration sensitivity by adding one or more braces either on the electrodes or on the layer of piezoelectric material.
Such conventional approaches to providing piezoelectric devices with desired elastic properties have several drawbacks. They are not truly design based, but rather require extra fabrication steps, such as adding or removing material from electrodes, or special operating environments, such as appropriate stiffening electrical fields. Generation of stiffening electrical fields may require additional circuitry. Conventional approaches typically also require the formation of various prototype devices to determine how to fabricate the piezoelectric device with a suitable rough state as described above. Further, conventional approaches are believed to work poorly where electrode thickness exceeds about two percent of total device thickness.
Patent application Ser. No. 09/212,816, entitled xe2x80x9cStiffness Effects in Piezoelectric Devicesxe2x80x9d, filed Dec. 16, 1998 provides a design-based system and method for verifying designs of piezoelectric devices during the design process and before any manufacturing steps are carried out. In particular, the system and method verifies whether the electrodes have the appropriate stiffness characteristics. With such a system and method extra fabrication steps and generation of special operating environments are avoided. The application also provides improved piezoelectric devices that meet final design specifications while reducing the need for post-production processing of the devices.
It is therefore an object of the present invention to provide further improvements in the designed-based analysis and verification of design parameters of piezoelectric devices.
It is another object of this invention to provide techniques for developing certain correction factors and using these correction factors in performing vibration frequency analysis of the piezoelectric material of the piezoelectric device which analysis can conveniently be performed before any manufacturing steps.
These correction factors are developed based on certain modeling equations which describe particular physical characteristics of the piezoelectric material, such as stress, strain, displacement and frequency, and are used to perform vibration frequency analysis of the piezoelectric material which may include, for example, determining fundamental thickness-shear frequency and coupling of the thickness-shear vibration mode with other vibrations modes such as the flexure vibration mode.
According to one aspect of the invention, a method is provided for verifying a design of a piezoelectric device which includes a piezoelectric material that preferably has a plate configuration and is made of AT-cut crystal. The method comprises forming a model of the piezoelectric material, wherein the model includes at least one correction factor; and analyzing the model of the piezoelectric material to determine one or more vibration frequency characteristics of the piezoelectric material to determine whether the piezoelectric material meets a design specification. Vibration frequency characteristics that are determined preferably include a fundamental thickness-shear frequency of the piezoelectric material and coupling characteristics between a thickness-shear vibration mode of the piezoelectric material and another vibration mode such as a flexural vibration mode. Preferably, the correction factor(s) is/are developed by forming a series of models of the piezoelectric material including a stress-strain model, a motion model based on the stress-strain model, and a frequency model based on the other two models.
In another aspect of the invention, the above-described method is implemented on an apparatus such as a computer system using hardware, software or combination thereof. When software is used, it is preferably embodied on a machine-readable medium such as a computer system or other processor-controlled device. When hardware is used to implement the invention, various circuit components including application specific integrated circuits (ASICs), digital signal processing circuits and the like may used.
In yet another aspect of the invention, a piezoelectric device is provided. The device comprises a piezoelectric material having a plate configuration and at least one electrode affixed thereto. A model of the piezoelectric material, including at least one correction factor, is formed and analyzed during a design of the device to determine one or more vibration frequency characteristics of the piezoelectric material to determine whether the piezoelectric material meets a design specification to reduce requirements for post-production processing of the device.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.